Gas fired ignitable fuel powered appliances are Known such as power tools, motor devices, or weapons where fuel is ignited by an electrical spark discharge. Such devices may be controlled by an electronic control circuit which is sensitive to noise.
It has been Known in such devices to interrupt the power to the control circuitry with a reset circuit as illustrated in prior art FIG. 1. Input 1 receives a trigger signal indicative of the electrical spark discharge for igniting the fuel. This trigger signal is connected through resistor 2 to a transistor 3 biased by a resistor 4 from a voltage source 5. This trigger signal switches transistor 3 so that at the output 6 power being supplied to the circuit is temporarily disconnected only while the trigger signal is present.
It is a disadvantage of the prior art circuit that transient noises or interferences may still remain even after an event such as fuel ignition by electrical spark discharge has occurred. Damage can still result to the control circuitry.
It is an object of the present invention to improve on the prior art reset circuits to provide further protection even after an initial triggering event has occurred.
The present invention provides an ordered and time controlled power interruption to a microcontroller or other logic control circuit or device controlling an application circuit or device. The invention has its primary and preferred use in an electronic control in a gas-fuel impact fastening power tool. However, it is applicable to any device controlled by electronic circuitry that may be sensitive to electrical noise caused by arcs or other events triggering damaging voltage or current pulses which may remain even after the trigger event. According to the invention, a microcontroller power removal reset circuit is provided (hereinafter known as the MPRRC) which is used both to maintain and remove electrical power from the application circuit.
The microcontroller ;power removal reset circuit (MPRRC) of the invention reduces or eliminates the risk of an electrical noise induced malfunction in a control logic system or microcontroller. It accomplishes this by causing a time related and time controlled removal of power to the protected circuit or device in response to some electrical event. The MPRRC thus removes power from the application circuit or device, stopping its operation during the electrical noise event. This eliminates the need for an electronic supervisory and fault recovery circuit commonly called a xe2x80x9cwatchdogxe2x80x9d circuit, as in the prior art.
It is a particular improvement of the invention that by providing a time delay element a time delay feature allows a waiting period for system transient noise to pass before power is reapplied to the application circuit. Prior art circuitry had no such time delay reset function. In the prior art, a transient noise can still be present when power is reapplied to the application circuitry.